The present invention relates to a heat-resistant thin film photoelectric converter and the preparation thereof.
A thin film photoelectric converter is used for a solar cell, photo-detector, photo-receptor for electrophotography, laser, electro-luminescent device, or the like. A thin film photoelectric converter contains fundamentally a layer of semiconductor and electrodes which come in contact with the layer of semiconductor. As an electrode, a transparent electrode and/or a metal electrode is used. As the material for the transparent electrode, there hitherto has been used a metallic compound such as ITO, ITO/SnO.sub.2, SnO.sub.2, In.sub.2 O.sub.3, Cd.sub.x SnO.sub.y (x=0.5 to 2, y=2 to 4), Ir.sub.z O.sub.1-z (z=0.33 to 0.5), or the like. A metal electrode of a metal such as Al, stainless steel, Fe, Ni, Cu, brass, Zn, Ag, or the like is provided on the semiconductor layer.
In FIG. 1, as an example of a photoelectric converter, a typical structure of a solar cell is illustrated. A solar cell has, as shown in FIG. 1, a transparent electrode 2 of a metallic compound (e.g. a metal oxide) on a transparent substrate 1 (e.g. glass), and thereon, a layer of p-type semiconductor 3, a layer of i-type semiconductor 4, and a layer of an n-type semiconductor 5 are provided. On the layer of n-type semiconductor 5, a layer of metal electrode 6 is provided as a back electrode. Light comes into the semiconductor layer through the transparent electrode and is absorbed by the semiconductor so as to generate electric power. A portion of the light is not absorbed in the semiconductor layer and reaches the back electrode and is reflected back to be absorbed in the semiconductor layer.
When a conventional solar cell is used at a temperature above about 50.degree. C., the metal (such as Al, Cu, brass, zinc, or Ag,) or the metallic compound of the electrodes is diffused to the semiconductor layer, so that the efficiency of the semiconductor is lowered. Especially, when an amorphous or microcrystalline semiconductor is used, the efficiency of the amorphous or microcrystalline semiconductor is notably lowered. For instance, in the case where the solar cell is used in the open air, the temperature at the surface of the solar cell reaches about 80.degree. C., so that the efficiency of the semi-conductor is remarkably lowered.
There are some metals which do not diffuse into the semiconductor layer when used as an electrode. Examples of such metals are Cr, Ni, Fe, and stainless steel. However, those metals have low electrical conductivity or low reflectivity compared with the above-mentioned metals such as Al, Cu, brass, Zn, and Ag. Thus, a solar cell having a back electrode of Cr, Ni, Fe, or stainless steel has a drawback due to ohmic loss in the electrode or poor reflection of light at the electrode. Any type of photoelectric converter, not only a solar cell, has the disadvantage described above when used at a high temperature.
An object of the present invention is to provide a heat-resistant thin film photoelectric converter, which does not suffer reduction of efficiency due to diffusion of metal or metallic compound from the electrode to the semiconductor layer, under the conditions that the ohmic loss in the back electrode and the loss of light due to poor reflection at the back electrode are not increased.